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Abstract: In order to understand the periodic and semi-periodic variations of luminousO- B- A-type stars, linear nonadiabatic stability analyses for radial andnonradial oscillations have been performed for massive evolutionary models$8M \odot - 90M \odot$. In addition to radial and nonradial oscillationsexcited by the kappa-mechanism and strange-mode instability, we discuss theimportance of low-degree oscillatory convection nonadiabatic g$^-$ modes.Although their kinetic energy is largely confined to the convection zonegenerated by the Fe opacity peak near $2\times10^5$K, the amplitude can emergeto the photosphere and should be observable in a certain effective temperaturerange. They have periods longer than those of the radial strange modes so thatthey seem to be responsible for some of the long-period microvariations of LBVsS Dor variables and $\alpha$ Cyg variables. Moreover, monotonously unstableradial modes are found in some models whose initial masses are greater than orequal to $60M \odot$ with $Z=0.02$. The monotonous instability probablycorresponds to the presence of an optically thick wind. The instabilityboundary roughly coincides with the Humphreys-Davidson limit.



Autor: Hideyuki Saio

Fuente: https://arxiv.org/







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